Technical Abstract:
Bacteriophage are viruses that prey on bacteria and may be a potential strategy to reduce foodborne pathogenic bacteria in the gastrointestinal tract of food animals. If phage are to be an effective intervention strategy, we must understand their role in the microbial ecology of the gut. Furthermore; for regulatory approval we need a better understanding of the incidence of phage in animals. Therefore the current study was designed to determine the incidence of phage active against Salmonella spp. in the feces of commercial finishing swine in the United States. Fecal samples (n=60) were collected from each of six commercial swine finishing operations. Samples were collected from 10 randomly selected pens throughout each operation. Total number of fecal samples collected in this study was n=360. Salmonella spp. were found in 4.6% of the fecal samples. Salmonella spp. were isolated from only 2 farms and the serotypes represented were Schwarzengrund, Anatum, Ohio and Heidelberg. Bacteriophages were isolated from fecal sample through 2 parallel methods: 1) initial enrichment in Salmonella Typhimurium, or 2) initial enrichment in E. coli B (a strain very sensitive to phages); followed by direct spot-testing against Salmonella Typhimurium. Bacteriophages active against Salmonella Typhimurium were isolated from 1.6% (6/360) of the individual fecal samples when initially enriched in Salmonella Typhimurium, but Salmonella Typhimurium-killing phages were isolated from 43.8% (158/360) of the fecal samples when first enriched in E. coli B. Our results indicate that bacteriophage capable of killing Salmonella Typhimurium are fairly widespread across commercial swine production facilities but may be at relatively low populations. These results indicates that phage (predator) populations may vary along with Salmonella (prey) populations and that phage could potentially be used as a food safety pathogen reduction strategy.